Double walled structural reinforcement

ABSTRACT

A double walled reinforcement structure and method for making a double walled reinforcement structure having a plurality of longitudinally extending and nested structural members. Each structural member comprises a first cell having a first cross-section and a second cell having a second cross-section. The second cell is positioned within the first cell and the second cell contacts the first cell in a plurality of locations to provide mutual support of the cells in a manner increasing the tensile and compressive strength of the structure.

TECHNICAL FILED

[0001] This application claims the benefit of U.S. patent applicationSer. No. 60/403144, filed Aug. 14, 2002 and is hereby incorporated byreference. This invention relates to a double walled structuralreinforcement, and more particularly to a structure having an inner cellwhich engages the outer cell at a plurality of locations in a mannerincreasing the strength and rigidity of the structure.

BACKGROUND OF THE INVENTION

[0002] Multi-celled structures are used in a wide variety ofapplications where light weight and relatively high strength structuresare needed to support and/or protect a particular item. One particularlyeffective structure is the honeycomb which comprises a plurality ofnested hexagonal structures. Bees use wax honeycomb to build hives tokeep their larvae safe. Aircraft manufacturers use aluminum honeycomb asa core material for aircraft control surfaces. Packagers use kraft paperhoneycomb to support and protect products during transportation. Thecellular form of honeycomb provides outstanding top-to-bottomcompression strength. Besides a high strength to weight ratio, otheradvantages include resistance to shock, high insulation value,cushioning, and low thermal conductivity factors.

[0003] While aluminum honeycomb has been mentioned as used in aerospaceapplications, another core material has gained considerable popularityin aerospace and commercial applications. NOMEX® honeycomb is alightweight, high strength, non-metallic honeycomb manufactured witharamid fiber paper. The aramid fiber paper is coated with a heatresistant phenolic resin. NOMEX® honeycomb has a higher shear strengthand much higher compressive strength than aluminum honeycomb and is usedin aircraft interiors, exteriors and other structural components.

[0004] However, several problems with NOMEX® and other honeycomb corematerials have been their susceptibility to water, delamination, andimpact resistance. Another problem is that strength of the structure islimited by the structure material, for example, a manufacturer may wantto use an aluminum honeycomb core but may need additional shear and/orcompression strength without adding significant weight to the structure.While honeycomb and other multi-celled structures provide a substantialbenefit to various industries, it would be advantageous to provide amulti-celled structure providing additional improvement over currentknown structures which overcomes one or more of these problems.

SUMMARY OF THE INVENTION

[0005] It is therefore an object of the present invention to provide anew structure that is even stronger than known structures. This andother advantages are provided by a structure comprising: a plurality oflongitudinally extending structural members, each structural membercomprising a first cell having a first cross-section selected from thegroup consisting of a polygon, an ellipse, and a circle, and a secondcell having a second cross-section selected from the group consisting ofa polygon, an ellipse, and a circle; wherein the second cell ispositioned within the first cell and the second cell contacts the firstcell in a plurality of locations to provide mutual support of the cells.

[0006] These and other advantages are also provided by a method ofmanufacturing a structure comprising the steps of: forming an inner cellhaving a first cross-section selected from the group consisting of apolygon, an ellipse, and a circle; forming an outer cell around theinner cell wherein the outer cell has a second cross-section selectedfrom the group consisting of a polygon, an ellipse, and a circle, suchthat the inner cell contacts the outer cell in a plurality of locationsto provide mutual support of the cells.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] This invention will now be described in further detail withreference to the accompanying drawings, in which:

[0008]FIG. 1 is a perspective view of a first embodiment of the presentinvention showing the double honeycomb cell configuration;

[0009]FIG. 2 is a perspective view of a second embodiment of the presentinvention showing the double rectangle cell configuration;

[0010]FIG. 3 is a perspective view of a third embodiment of the presentinvention showing the double triangle cell configuration;

[0011]FIG. 4 is a perspective view of a third embodiment of the presentinvention showing a triangle and circle cell configuration;

[0012]FIG. 5 is a cross-sectional view an outer cell mold for use inmaking a formed corrugated sheet in accordance with an embodiment of themethod of the present invention;

[0013]FIG. 6 is a cross-sectional view an inner cell mold for use inmaking a formed corrugated sheet in accordance with an embodiment of themethod of the present invention;

[0014]FIG. 7 is an end view of an outer cell mold having a mold baseplate and one top mold plate of an inner cell mold for use in making aformed corrugated sheet in accordance with an embodiment of the methodof the present invention;

[0015]FIG. 8 is an end view of an inner cell mold having a mold baseplate and one top mold plate of an inner cell mold for use in making aformed corrugated sheet in accordance with an embodiment of the methodof the present invention;

[0016]FIG. 9 is a perspective view an inner cell mold showing the moldbase plate and a plurality of top mold plates;

[0017]FIG. 10 is a perspective view of the prepreg sheet in a cell moldshowing the mold base plate and a plurality of top mold plates;

[0018]FIG. 11 is a perspective view of the molds placed in an oven;

[0019]FIG. 12 is a graph of a curing cycle for a particular corematerial;

[0020]FIG. 13 is a perspective view of the formed material in the moldwith some of the top mold plates removed;

[0021]FIG. 14 is a perspective view adhesive applied to the formedmaterial;

[0022]FIG. 15 is an exploded end view and an assembled end view of adouble walled hexagonal structure in accordance with an embodiment ofthe present invention;

[0023]FIG. 16 is a perspective view of the machining of the doublewalled hexagonal structure to its final form; and

[0024]FIG. 17 is an alternate method of forming the corrugated sheetsused in a method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0025] This invention will now be described in detail with reference tovarious embodiments thereof. Referring now to FIG. 1, a first embodimentof the structure 10 of the present invention is shown comprising aplurality of longitudinally extending structural members 20, eachstructural member comprising a first cell 30 having a polygonalcross-section in the form of a hexagon, and a second cell 40 having asecond polygonal cross-section. Each cell 30, 40 has a plurality oflinear walls 32, 42, and a plurality of corners 34, 44. The second cell40 is positioned within the first cell 30 and the second cell 40contacts the first cell 30 in a plurality of locations 50 to providemutual support of the cells 30, 40. More particularly, the second cellis rotated with respect to the first cell at an angle Θ such that thecorners 44 of the second cell 40 contact the walls 32 of the first cell30. The angle 0 is preferably one hundred eighty degrees divided by thenumber of sides of the polygon. However it is also contemplated thatother angles of rotation may be used which provide a non symmetricdistance between the contact point of the second cell 40 on the linearwall 32 of the first cell 30 and the corners 34 adjacent the linear wall32.

[0026] While the corners 44 may merely be in contact with the linearwalls 32 to be effective, it is also contemplated that the corners 44may be attached or bonded to the linear walls 32 to provide additionalstrength. It is also possible to extrude or mold the cells 30, 40 suchthat the walls 32, 42 of the plurality of structural members 20 areintegrally interconnected.

[0027] Although the cells 30, 40 are shown as hexagons, the invention isnot intended to be limited as such and the cells may be any appropriateshape including other polygons (triangles 30′, 40′, rectangles 30″, 40−,pentagons 30′″, 40′″, etc.) or may be a circle or an ellipse. FIG. 2shows a double rectangle or square cell configuration; FIG. 3 shows adouble triangle cell configuration; while FIG. 4 shows a possiblecombination of dissimilar shapes such as a first cell in the form of atriangle and a second cell in the form of a circle.

[0028] The plurality of structural members 20 are nested together, whichin the case of the hexagonal first cells 30 provides a honeycombstructure. As the members are nested, each discrete cell 30 has at leastone linear wall 32 registering against a linear wall of an adjacentcell. Additionally, the corners 42 of the second cell 40 are positionedadjacent corners 42 of an adjacent second cell 40. In this manner thestructure 10 reinforces itself wherein the second cell 40 is reinforcedby the first cell 10 and vise versa, as well as by adjacent first 30 andsecond cells 40. In another embodiment it is also contemplated that atleast one linear wall 32 is shared by adjacent cells 30 such that theplurality of structural members are all interdependent such as in a truehoneycomb.

[0029] As previously mentioned, the double cell configuration of thepresent invention can be manufactured using a molding process, anexample of which will now be discussed in greater detail. As shown inFIGS. 5-9, the double cell mold 50 comprises an outer cell mold 60 andan inner cell mold 70. In one embodiment, the molds are manufacturedfrom steel such as typical low carbon free machining steel, however, anysuitable material may be used and the invention is not intended to belimited to a particular mold material. The outer cell mold 60 comprisesa bottom base 62 and a plurality of longitudinal top mold members 64which may be secured to the bottom base 62. The outer cell mold 60 isconfigured to produce a sheet 68 comprising a plurality half hexagonalcells 66 having a three full linear walls 32. After being removed fromthe molds 60 and as discussed below with relation to FIG. 15, two sheets68 of the pluralities of half hexagonal cells 66 may be placed on top ofeach other and secured by an adhesive to form a plurality of hexagonalfirst cells 30, each cell having six full linear walls 32. Each of thecells 30 are separated from each other by a linear wall 32 whichprovides a space for nesting additional cells 30. Similarly, the innercell mold 70 comprises a bottom base 72 and a plurality of longitudinaltop mold members 74 which may be secured to the bottom base 72. Theinner cell mold 70 is configured to produce a sheet 78 comprising aplurality of half hexagonal cells 76 having two full linear walls 42positioned between two linear wall segments 45. Two pluralities of halfhexagonal cells 76, are placed on top of each other and secured by anadhesive to form a plurality of hexagonal second cells 40 having sixfull linear walls 42. It is noted that the inner cell mold 70 produceshalf hexagonal cells 76 that are rotated fifteen degrees from the halfhexagonal cells 66 produced by the outer mold 60. It is alsocontemplated that the half hexagonal cells 76 may either be slightlysmaller than the half hexagonal cells 66 produced by the outer mold 60to allow for clearance, or the half hexagonal cells 76 may be the samesize as the half hexagonal cells 66 produced by the outer mold 60 toallow for the adhesive thickness between the sheets 68, 78. Having equalsized inner and outer cells 76, 66 may also provide a preloadedinterference fit between the cells which may enhance their physicalproperties. Accordingly, a plurality of structural members 20 may beproduced by placing the two sheets 78 of half hexagonal cells 76 betweenthe two sheets 68 of rotated half hexagonal cells 66.

[0030] The material used in molding the double cell configuration of thepresent invention can be any suitable moldable material. In oneembodiment of the invention, an advanced composite material may be usedcomprising an epoxy resin prepreg reinforced with unidirectional carbonfibers. Referring now to FIG. 10, a sheet 80 of prepreg material isplaced over the bottom base 62 of the mold 60. The longitudinal top moldmembers 64 are individually positioned and pressed one at a time bysecuring the top mold member 64 to the bottom base 62. This allows theprepreg material 80 to properly form inside the mold cell groove orcavity. Once all the top mold members 64 are properly positioned andsecured to the bottom base 62, the mold 60 is placed in an oven 55 (seeFIG. 11) and cured based on a suitable prepreg temperature curing cyclesuch as that shown in FIG. 12. After the part is cured, the part isdemolded by removing the top mold members 64 from the bottom base 62 asshown in FIG. 13. The process is the same for the inner and the outercells 40, 30. An adhesive 82 is applied to the molded sheets 68, 78 ofhalf cells to form a completed sheet of cells as shown in FIG. 14. Incompleting the double cell configuration of the present invention, theinner cells 30 are formed first by adhering two molded sheets 78 of theinner half cells. The outer cells 40 are then formed by adhering onemolded sheet 68 of outer half shells to the top sheet 78 of inner cells30 and adhering one molded sheet 68 of outer half shells to the bottomsheet 78 of the inner cells to form a sheet 88 of double hexagonalcells. Adhesive 82 may be applied to the outer portions 78 of sheet 88to position and secure multiple sheets 88 in the nested manner to form adouble wall honeycomb structure 10 as best shown in FIG. 15.

[0031] One particular adhesive that has been found to be effective is atwo-part epoxy adhesive comprising a resin and a curing agent such as815C Epon resin and 3140 EPI-Cure curing agent manufactured by Shell. Itis also contemplated that the properties of the adhesive may be improvedwith one or more additives. An example of such is the addition ofcatalytic multi-wall carbon nanotubes which have been found to increasethe modulus of the epoxy adhesive as well as decreasing the moistureabsorption of the epoxy adhesive. Although an example of a particularadhesive has been discussed, the invention is not intended to be limitedas such and any suitable adhesive or means for attaching the cells toone another is contemplated such as welding, thermal fusion bonding,etc.

[0032] The double wall honeycomb structure 10 can then be machined toits final dimensions (see FIG. 16) and subjected to any post processingwhich may be used to enhance the physical characteristics of thestructure 10. For example, in applications where the structure 10 issubjected to water, it is contemplated the cells may be partially orcompletely filled with a water resistant material. The first and secondcells 30, 40 may alternatively be coated with a water resistantsubstance. Particular attention may be paid to machined surfaces which,depending on the core material used, may need to be coated with aprotective substance to inhibit water ingress, corrosion, or otherfactors which may inhibit the performance of a particular core materialin a particular application.

[0033] Although the core material discussed above is an epoxy resinprepreg, the invention is not intended to be limited to a particularcore material. It is contemplated that the double cell configuration ofthe present invention can be manufactured of the same materialscurrently being used in prior art structures such as metallic,polymeric, ceramic, and other non-metallic materials such as paper(NOMEX®) or corrugated cardboard. The repeated structure of the dualwalled cells may be manufactured using forming techniques, corrugatedforming processes, extruding, molding or any other appropriatemanufacturing technique. A corrugated process utilizing a corrugatedroller 90 is used to form honeycomb sheets 68 is shown in FIG. 17 whichcan be used with materials such as NOMEX® paper, aluminum, or other suchformable materials. It is contemplated that a second set of corrugatedrolls 92 having teeth similar to the profile of the inner mold 70 may beused to produce corrugated sheets 78 to produce the inner cells 40 ofthe double cell structure 10 of the present invention. Adhesive wouldthen be applied to the sheets, and the sheets would then be stacked inthe same manner as the molding method discussed above and shown in FIG.17.

[0034] Another advantage of the present invention is that the secondcell 40 provides additional locations or surface area for bonding to acover material (not shown) on either end of the structure 10. Theadditional bonding helps prevent delamination of the cover material fromthe ends of the cells 30, 40. The second cell 40 also increases theshear strength and the compression strength of the structure 10 and alsoincreases the impact resistance of the structure 10.

[0035] It is further contemplated that the first cell 30 may bemanufactured of a first material having first material properties, whilethe second cell 40 may be manufactured of a second material havingsecond material properties. This feature will allow the structure 10 tobe engineered toward a particular application in which multiplematerials may have favorable characteristics when used in combinationwhich may not be present when using only one of the first and secondmaterials.

[0036] New continuous/semi-continuous processes are currently beingdeveloped for producing honeycomb panels. Examples of these processesinclude rotational and continuous thermoplastic honeycomb panelproduction lines. It is contemplated that these processes may be adaptedto create the double walled honeycomb structure of the presentinvention.

[0037] Although the present invention has been described above indetail, the same is by way of illustration and example only and is notto be taken as a limitation on the present invention. Accordingly, thescope and content of the present invention are to be defined only by theterms of the appended claims.

What is claimed is:
 1. A structure comprising: a plurality oflongitudinally extending structural members, each structural membercomprising a first cell having a first cross-section selected from thegroup consisting of a polygon, an ellipse, and a circle, and a secondcell having a second cross-section selected from the group consisting ofa polygon, an ellipse, and a circle; wherein the second cell ispositioned within the first cell and the second cell contacts the firstcell in a plurality of locations to provide mutual support of the cells.2. The structure of claim 1, wherein the first cell is a polygon and thesecond cell is a polygon wherein the first and second polygon each havea plurality of corners and linear walls therebetween; wherein theplurality of corners of the second polygon contact the linear walls ofthe first polygon.
 3. The structure of claim 2, wherein eachlongitudinally extending structural member has at least one linear walladjacent a corresponding linear wall of an adjacent longitudinallyextending structural member.
 4. The structure of claim 2, wherein eachlongitudinally extending structural member shares at least one commonlinear wall with an adjacent longitudinally extending structural member.5. The structure of claim 2, wherein the first polygon and the secondpolygon have the same number of sides.
 6. The structure of claim 5,wherein the second polygon is rotated at an angle of 180/X with respectto the first polygon, wherein X is the number of sides of each polygon.7. The structure of claim 5, wherein the walls of the second polygon oneither side of each contact point are positioned at equivalent angles tothe adjacent wall of the first polygon.
 8. The structure of claim 2,wherein the walls of the second polygon on either side of each contactpoint are positioned at an angle to the adjacent wall of the firstpolygon.
 9. The structure of claim 1, wherein the plurality oflongitudinally extending structural members are manufactured from acorrugated material.
 10. The structure of claim 1, wherein the pluralityof longitudinally extending structural members are manufactured from ametallic, polymeric, or non-metallic material.
 11. The structure ofclaim 1, wherein the plurality of longitudinally extending structuralmembers are contained within two planar members.
 12. The structure ofclaim 1, wherein the second cell is attached to the first cell at theplurality of contact locations between the second cell and first cell.13. The structure of claim 1, wherein the dimensions of the first cellare substantially different from the dimensions of the second cell. 14.The structure of claim 1, wherein the first cell is a polygon and thesecond cell is a circle or ellipse; wherein the polygon has a pluralityof linear walls; wherein the second cell contacts each linear wall ofthe polygon.
 15. The structure of claim 14, wherein each longitudinallyextending structural member has at least one linear wall adjacent acorresponding linear wall of an adjacent of longitudinally extendingstructural member.
 16. The structure of claim 1, wherein the first celland the second cell are hexagons.
 17. The structure of claim 16, whereinthe longitudinally extending structural members form a double walledhoneycomb structure.
 18. A method of manufacturing a structurecomprising the steps of: forming an inner cell having a firstcross-section selected from the group consisting of a polygon, anellipse, and a circle; forming an outer cell around the inner cellwherein the outer cell has a second cross-section selected from thegroup consisting of a polygon, an ellipse, and a circle, such that theinner cell contacts the outer cell in a plurality of locations toprovide mutual support of the cells.
 19. The method of claim 1, furthercomprising the step of attaching the inner cell to the outer cell.
 20. Amethod of manufacturing a structure comprising the steps of: forming aplurality of sheets of material into a first corrugated configurationforming a plurality of sheets of material into a second corrugatedconfiguration attaching two of the plurality of sheets of the firstcorrugated configuration to form a series of first polygonal cells.attaching one of the plurality of sheets of the second corrugatedconfiguration to each exterior side of the attached two sheets of thefirst corrugated configuration such that the sheets of the secondcorrugated configuration form a series of second polygonal cells,wherein the first polygonal cells are positioned within the secondpolygonal cells and are configured rotated at a predetermined angle withrespect to the second polygonal cells.
 21. The method of claim 20further comprising the steps of: attaching additional sheets of thefirst and second corrugated configuration such that the sheets of thesecond corrugated configuration form second polygonal cells that arepositioned in a nested configuration, each having a first polygonal cellpositioned within the second polygonal cell and configured rotated at apredetermined angle with respect to the second polygonal cell.
 22. Themethod of claim 20, wherein the polygonal cells are hexagons.
 23. Themethod of claim 20, wherein the step of forming the sheets into thefirst and second corrugated configuration is accomplished using a firstand second mold.
 24. The method of claim 20, wherein the step of formingthe sheets into the first and second corrugated configuration isaccomplished using a first and second set of corrugated rolls.
 25. Themethod of claim 20, wherein the step of attaching the form sheets ofmaterial to each other is accomplished using an adhesive.
 26. The methodof claim 20, wherein the step of attaching the form sheets of materialto each other is accomplished by welding or thermal fusion.
 27. Themethod of claim 20, further comprising the step of forming the sheetscomprises the steps of inserting the sheets into a mold, placing themold in an oven, curing the sheets, removing the mold from the oven, andremoving the formed sheets from the mold.
 28. The method of claim 20,further comprising the step of providing a plurality of epoxy resinprepreg sheets.
 29. The method of claim 21, further comprising the stepof machining the structure to its final form.
 30. A method ofmanufacturing a structure comprising the steps of: providing a pluralityof sheets of material each having a first side and a second side;forming a first and a second sheet into a series of five repeatingsurfaces, wherein the second surface is generally 90 degrees from thefirst surface, the third surface is generally 120 degrees from thesecond surface, the fourth surface is generally 120 degrees from thethird surface, and the fifth surface is generally 120 degrees from thefourth surface, wherein the second and fourth surfaces are generallyparallel to each other; forming a third and a fourth sheet into a seriesof four repeating surfaces each formed generally 120 degrees from eachother, wherein the first surface and the third surface are generallyparallel to each other and the second and fourth surface are formed atan included angle of approximately 60 degrees; attaching the second sideof the first sheet to the second side of the second sheet such that thesecond, third, fourth, and fifth surfaces of the first and second sheetform a hexagon separated from adjacent hexagons by the first surface;attaching the second side of the third sheet to the first side of thefirst sheet attaching the second side of the fourth sheet to the firstside of the second sheet such that the second, third, and fourthsurfaces of the third and fourth sheet form a hexagon separated fromadjacent hexagons by the first surface.
 31. The method of claim 30,wherein the step of forming the plurality of sheets is accomplished in amolding process.
 32. The method of claim 31, wherein the molding processcomprises the following steps: providing a first and second mold whereinthe first mold is used to form the first and second sheets and thesecond mold is used to form the third and fourth sheet, each mold havinga mold base and at least one top mold member; placing one of theplurality of sheets on the first mold base and placing another of theplurality of sheets on the second mold base; sequentially positioning,pressing, and securing each of the at least one top mold members to themold bases; placing the first and second mold into an oven and curingthe sheets; removing the first and second mold from the oven andallowing the sheets to cool; and removing the formed sheets from themolds.
 33. The method of claim 30, wherein the step of forming theplurality of sheets is accomplished using corrugated rollers.
 34. Themethod of claim 30, wherein the steps of attaching the plurality ofsheets to each other is accomplished by using an adhesive.
 35. Themethod of claim 30, wherein the steps of attaching the plurality ofsheets to each other is accomplished by welding.
 36. The method of claim30 further comprising the steps of: forming a fifth and sixth sheet intoa series of five repeating surfaces, wherein the second surface isgenerally 90 degrees from the first surface, the third surface isgenerally 120 degrees from the second surface, the fourth surface isgenerally 120 degrees from the third surface, and the fifth surface isgenerally 120 degrees from the fourth surface, wherein the second andfourth surfaces are generally parallel to each other; forming a seventhsheet into a series of four repeating surfaces each formed generally 120degrees from each other, wherein the first surface and the third surfaceare generally parallel to each other and the second and fourth surfaceare formed at an included angle of approximately 60 degrees; attachingthe second side of the fifth sheet to the second side of the sixth sheetsuch that the second, third, fourth, and fifth surfaces of the fifth andsixth sheet form a hexagon separated from adjacent hexagons by the firstsurface; attaching the first side of the sixth sheet to the first sideof the third sheet such that the hexagons formed by the fifth and sixthsheets are adjacent the first surfaces of the third sheet and the firstsurfaces of the third sheet and the first surfaces of the sixth sheetare adjacent the third surfaces of the third sheet; attaching the secondside of the seventh sheet to the first side of the fifth sheet such thatthe second, third, and fourth surfaces of the seventh sheet and thefourth, first, and second surfaces of the third sheet form a hexagonnested between the hexagons formed by the third and fourth sheets.